This invention relates to pocketed spring assemblies for mattress cores and the like and to a method of assembling pocket coil spring assemblies.
It is known to place strings of pocketed or encased coil springs in a parallel fashion to create a mattress, inner spring assembly or other body support foundation. A known method for making the strings of encased coil springs is to fold the encasing or pocketing material such that there is a crease on one longitudinal side and an opening on the opposite side. Compressed coils are inserted through the opening between the layers of pocketing material and the opening is sealed by a sealing system, such as a thermal sealing system or stitching. The layers of pocketing material are further sealed between each coil. The coils are than turned and expanded such that one end of the coil is facing the crease of the pocketing material and the other end is facing the sealed opening.
The number of coils in a string or row and the number of rows are dependent upon the coil spring diameter and the desired finished size of the mattress or the like. The construction of the mattress core may include a plurality of rows of parallel coils with the coils aligned in columns so that the coils line up in both longitudinal and lateral directions, or they may be nested in a honeycomb configuration wherein coils in one row are off-set from coils in the adjacent row.
It is known to connect the strings of coils in a coil to coil manner by applying an adhesive to the encased coils as illustrated in Stumpf U.S. Pat. Nos. 4,566,926 and 4,578,834 and Suenens et al. Nos. 5,016,305 and 5,637,178, each of which are hereby incorporated by reference. Nested constructions where strings of coils are interlocked are illustrated in Stumpf U.S. Pat. No. 5,319,815 and German 4,040,220, each of which are hereby incorporated by reference. Other methods of connecting the strings of coils utilize metal clips known as hog rings or they may be stitched with twine which penetrates each string of coils.
Another method in the prior art is the use of strings of coils positioned in a frame with a web of nonwoven material on the top and bottom of the pocketed coil units. Alternatively, or in addition, beads of hot melt adhesive may be dispensed onto the top and bottom surfaces of the strings of coils and a sheet of nonwoven material pressed against the adhesive containing surfaces.
In the prior art processes, control and distribution of the adhesive is difficult and inefficient. Some areas of the coil strings may receive too much adhesive while other areas may not receive a sufficient amount of adhesive. Excess adhesive of course is economically inefficient, while risk of separation of the pocketed coil strings from the nonwoven material may result from too little adhesive. Moreover, when adhesive is sprayed there is a tendency for the spray nozzles to clog so that the flow of glue is obstructed. This results in a time consuming cleaning and maintenance program. Additionally, hot melt spraying requires the system to be heated about one hour before spraying can begin. Other difficulties presented by hot melt spraying and application of beads is that the hoses through which the hot melt flows must be insulated to maintain the temperature of the glue within the hose, thereby resulting in very heavy hoses. If the spraying process involves manually moving the spray nozzle to which the hose is attached to spray the adhesive, the heavy hoses result in the process being slow and fatiguing to the operators who often encounter minor burns from the glue and the nozzles.
A potential solution for at least some of the above-described disadvantages is disclosed in this inventor""s pending U.S. patent application Ser. No. 09/024,536, filed Feb. 17, 1998, and hereby incorporated by reference in its entirety. In that method, the plurality of strings of pocketed coil springs are placed between top and bottom sheets of nonwoven webs of material, each web having a heat activated reinforcement netting. Thus, the strings are attached at their upper and lower surfaces to the sheets of material, rather than on their side surfaces to an adjacent string.
A problem that exists in many prior art processes is the tendency of the rows of pocketed coil springs to expand and contract in the longitudinal direction of the string which causes a deformation or inconsistent sizing of the spring assembly. Even though the adjacent strings of pocketed coil springs are adhesively bonded, connected or otherwise joined together, slack in the fabric of the individual or collective strings allows the spring assembly to expand and contract and thereby produce an inconsistently sized or dimensioned spring assembly as a result of manufacturing production of pocketed coil spring assemblies. In other words, spring assemblies having the same number of pocketed springs and the same number of strings of pocketed springs may be larger or smaller than similar units. This presents difficulties in the production of mattresses and the like utilizing such spring assemblies.
One attempt to minimize this deformation problem has been to cover the spring assembly on the top and/or bottom of the springs as previously described. However, while this approach may minimize the deformation or dimensional inconsistency of the spring assembly, it also inhibits the individual deflection of the various coil springs in the pockets. As a result, certain benefits which are afforded by a pocketed coil spring assembly are not available with this approach to solving the deformation problem.
The present invention provides a spring assembly, and a method for making the same, having a layer of preferably fabric material which may or may not include an adhesive component between strings of pocketed coil springs, thus serving to adhere the strings to each other while reducing or preventing wear between coils in frictional relation. According to the principles of the present invention, the fabric layer may be added to one or both sides of the pocketing material during the encasing process. The strings of pocketed coil springs are assembled in side-by-side relation and the adhesive component of the fabric material is activated, thereby bonding the strings together. A feasible and economic method for adhering strings of pocketed coil springs together in a spring assembly is provided. Further, a significant advantage of a presently preferred method and resulting spring assembly according to this invention is the ability to consistently size the spring assembly by tautening the fabric material or netting which is positioned between the adjacent strings.
The fabric material or adhesive netting, which is interposed between the adjacent strings of pocketed coil springs, has low stretching properties and when it is pulled taut and adhered or bonded to facing surfaces of the strings, it minimizes, reduces and/or eliminates the tendency for the strings and resulting spring assembly to expand and/or contract in the longitudinal direction of the strings. The layer which is interposed bet ween the adjacent strings may comprise, according to one presently preferred embodiment of this invention, a netting of adhesive which, when activated, is bonded to each of the confronting surfaces of the adjacent strings of pocketed coil springs to thereby form the spring assembly and minimize or prevent the pocketed coil springs in each string from moving toward or away from one another and the resulting contraction or expansion of the spring assembly in that direction. The layer of fabric, netting or material which is interposed between the strings and pulled taut may be formed of a nonwoven, woven or knitted fabric. The layer itself may include an adhesive component according to one embodiment of this invention or adhesive may be added to bond the layer and adjacent strings together.